1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device including a thin film transistor, a light-emitting element, a passive element, and the like. Furthermore, the present invention relates to an electro-optical device represented by a liquid crystal display panel, a light-emitting display device that have a light-emitting element, and an electronic device in which an IC tag, by which information can be transmitted and received wirelessly, are mounted as components.
It is to be noted that “a semiconductor device” in the present specification refers to a general device that can function as a semiconductor device using semiconductor characteristics, and an electro-optical device, a light-emitting device, a semiconductor circuit, an IC tag, and an electronic device can all be considered semiconductor devices.
2. Description of the Related Art
In recent years, technology that is used to form a thin film transistor using a thin semiconductor layer (with a thickness of from several nanometers to several hundreds of nanometers, approximately) that are formed over a substrate that have an insulating surface has been attracting attention. A thin film transistor has been widely applied to electronic devices such as an IC and an electro-optical device, and their development especially as a switching element for an image display device has been particularly urgent.
With applications that use such an image display devices, a variety of things are being expected, and use in portable devices is particularly attracting attention. A glass substrates and a quartz substrate are often used in an image display device; however, there are disadvantages to using the glass substrate and the quartz substrate in that they are easily breakable as well as heavy. Furthermore, increasing the size of a glass substrate and a quartz substrate is difficult for mass production, and the glass substrate and the quartz substrate are thus not suitable for mass production. For these reasons, forming a thin film transistor over a flexible substrate, typically, a flexible plastic film, is being attempted.
Thus, technology in which a semiconductor element including a thin film transistor, that are formed over a glass substrate is separated from the glass substrates and transferred to another substrate, for example, to a plastic film or the like, has been proposed.
In Patent Reference Document 1, a separation technique by which a silicon oxide layer that is to be used as a separation layer is removed by wet etching is disclosed. In addition, in Patent Reference Document 2, a separation technique by which a silicon layer that is to be used as a separation layer is removed by dry etching is disclosed.
In Patent Reference Document 3, a technique where a metal (Ti, Al, Ta, W, Mo, Cu, Cr, Nd, Fe, Ni, Co, Ru, Rh, Pd, Os, or Ir) layer is formed over a substrate, an oxide layer is formed and stacked thereover, a metal oxide layer of the metal layer is formed in the interface between the metal layer and the oxide layer, and separation is performed during a subsequent step using this metal oxide layer is disclosed.    Patent Reference Document 1: Published Patent Application No. H8-288522    Patent Reference Document 2: Published Patent Application No. H8-250745    Patent Reference Document 3; Published Patent Application No. 2003-174153